1. Field of the Invention
This invention relates to a method of coating liquid coating compositions of various kinds in which one or more layers of liquid coating composition are applied to a moving support which is in the form of continuous web (hereinafter referred to as "web") in the manufacture of, e.g., photographic films, photographic papers, magnetic recording tapes, adhesive tapes, pressure sensitive recording papers, offset printing papers, etc. More particularly, the invention relates to a method of preventing a thick coating of a liquid coating composition encountered at the time of starting the coating.
2. Description of the Prior Art
In conventional methods in which the coating of a liquid coating composition of various kinds on a web is started, as shown in FIG. 1, even if the liquid coating composition 2 should come into; contact with the web 1 moving in the direction as indicated by the arrow A, generally the liquid coating composition 2 would not immediately be coated on the web 1, but it will be coated on the web 1 after the passage of a section (l) of the web between where coating is started and where the coating composition actually is laid on the web. In this instance, it has been known that the coated film in the vicinity of a line (hereinafter referred to as "coating start line") 3 formed by joining points wherein the liquid coating composition 2 is initially applied to the web 1 has a coating thickness ranging from about 5 to 100% above that of other portions of the web. This coating start line does not always appear in the form as illustrated in FIGS. 1 (a), (b) and (c), but may often assume complicated shapes. A number of studies has been made on various aspects to find the cause of this difficulty at the time of starting the coating, but an established theory has not yet been found and clarified. Although an explanation has often been offered that the liquid coating composition 2 does not adhere to the web 1 until the web 1 is sufficiently wetted, such an explanation may not have be persuasive as a result of observing the phenomenon in all its aspects. Under the present conditions, means of minimizing such a difficulty encountered at the time of starting the coating do not exist since the cause of the difficulty is not clear. Unless such a difficulty encountered at the time of starting the coating is eliminated, a period of time for the drying process for drying the thickly coated film in the vicinity of the coating start line should be prolonged notwithstanding the fact that the thickly coated portion is only a portion of the entire area. In addition, if the thickly coated portion is not sufficiently dried, a part of the undried coated film remains on a reversing roller or the like after the drying step has been completed, resulting in contamination in the steps, thereafter a disturbance of the surface of the coated film, and a marked loss of value in the product. Thus, this difficulty poses a significant problem.